With the mailing list thread is included a jstack stack trace to illustrate the deadlock.

A deadlock occurs when a Mina StateMachine's Filter (A) reads data using messageReceived() while another mina StateMachine's Filter (B) write data at the same time using filterWrite().

My current oberservation show that what witch I thought only occured rarely happens in fact very frequently when there are few concurrent connections! (Basically the faster we can get a response to a request, the more likely the chance of this situation happening!)

The effect of such a deadlock is that it freezes the whole application without possibility of recovering.